Numerous prosthetic joints have been developed for replacing finger joints, although most such joints have involved the replacement of the joint where the finger joins the hand, namely the joint between the proximal phalanx and the metatarsal. These latter joints typically involve some type of captivated ball-and-socket arrangement for permitting a substantial range of pivoting movement in a vertical plane, while sometimes also permitting a limited sideward displacement in an attempt to provide for motion which more closely correlates with the natural joint. Joints of this latter type, however, are normally not suitable for replacing the proximal or distal phalangeal joints of the finger inasmuch as these latter replacement joints typically possess a structure which is undesirably large and complex for replacing the phalangeal joints, and in addition these latter joints do not require and in fact do not desire any capability of providing a sideward or lateral pivoting.
Examples of finger joints which are designed specifically for replacing the human joint located between the metatarsal and the proximal phalanx are disclosed by U.S. Pat. Nos. 3,946,445, 4,242,759 and 4,231,121, although the joint of this latter patent is also disclosed as being suitable for use as a PIP (phalangeal-interphalangeal) or DIP (distal-interphalangeal) joint.
Accordingly, the present invention relates to an improved joint which is designed specifically for use in replacing the human joint located between the proximal and intermediate phalanx (a PIP joint), or between the intermediate and distal phalanx (a DIP joint). The improved prosthetic joint of this invention is particularly of a small and compact structure to permit its surgical implantation so as to replace the natural joint, with the joint being implantable in such a manner as to facilitate its attachment to the phalanx while at the same time providing a vertical range of pivoting movement which closely approximates the natural joint movement while restricting undesired sideward movement.
In the improved implant joint of this invention, the joint is defined by two one-piece implant members, one comprising essentially a cap member having a configuration which roughly resembles a semicylindrical shell-like element which has a substantially planar rearward extension associated with the lower edge thereof, whereby the member can be attached to the distal end of the respective phalanx and oriented so that the outer substantially semicylindrical surface of the member is generated about a substantially horizontal axis. The outer surface of the member has a substantially centrally located groove extending therearound for accommodating a rib on the other implant member to prevent relative sideward pivoting between the joint members. The other joint member includes an enlarged head secured to one end of a tack which has deformable flanges so that the tack can be inserted into and lockingly secured to the proximal end of the adjacent phalanx. The enlarged cap on this other implant member has a pair of sidewardly spaced part-spherical surfaces which are mirror images of one another and are effectively separated by an intermediate ridge, which ridge projects into the groove on the first member. The bearing surfaces on the first member have a configuration which, in transverse cross section, corresponds to the bearing surfaces on the second member so as to permit free and smooth slidable support and contact between the first and second members, with the slidable contact restricting relative movement between the members to pivoting movement substantially within a vertical plane.
Other objects and purposes of the improved joint according to the present invention will be apparent to persons familiar with joints of this general type upon reading the following specification and inspecting the accompanying drawings.